If you want to become acquainted with the culture and history of the island, you should definitely visit Asclepion, which was an ancient healing center dedicated to God Asclepius. Here is where Hippocrates, the father of modern medicine (whose oath of Ethics, the Hippocratic oath, is still taken by graduate medicine students all over the world) founded his school and taught medicine. Speaking of Hippocrates, you can also visit the Plane tree of Hippocrates in the city center, another spot where, according to tradition, Hippocrates himself taught medicine. Other places of great archaeological significance in Kos are the Ancient Agora and the Ancient Gymnasium with the Acropolis, the Hippodrome and the Nymphaeum.
The Castle of the Knights, otherwise known as Nerantzia Castle, is very popular due to its impressive architectural design.
Live a unique experience on the island by visiting the hot springs in Agios Fokas which are well-known for their therapeutic effect on various illnesses and mostly, skin ailments.
Another wonderful place that you should not miss out is the islet of Kastri, which can be seen opposite Kefalos beach. On top, there is a small castle that used to protect the islet from pirates and on one side of the island, there is a small church dedicated to Saint Nicolas, the protector of sailors.